The present invention relates generally to the manufacture of fibrous webs and, more particularly, to a method and an apparatus for making a reinforced, dry laid fibrous web.
A dry or air laid mat of cellulosic fibers typically exhibits relatively low strength and low stretch characteristics. As a result of these low strength and stretch characteristics, the mat is relatively difficult to process in subsequent paper making steps. Typically, the final air or dry laid cellulosic product also possesses these low strength and stretch characteristics. As a result, the present inability of the art to achieve the desired strength and stretch properties in the final dry laid, fibrous web product often limits the use of the web product.
Various techniques have been proposed to attempt to remedy these low strength and stretch properties in dry laid fibrous webs. These techniques include the addition of water to the web for the hydrogen bonding of the fibers, the inclusion of a scrim within the web, and the addition of thermoplastic bonding materials to the web.
Although these techniques may improve somewhat the strength and stretch characteristics of a dry laid fibrous web, these techniques typically do not increase the bulk of the web. The lack of bulkiness in the web product inhibits the use and marketability of the web product. Consumers and commercial users generally desire a web product that provides bulk, as well as strength and stretchability. Typically, bulk in a web product enhances the absorbency and liquid holding capacity of the web product in comparison to a relatively non bulky web product. Moreover, consumers and commercial users usually prefer the handling or feel of a relatively bulky web product. When the web product is used as a tissue, towel, wiper, or other simulated cloth-like material, it is especially desirable for the web product to possess bulk as well as strength and stretchability.
As noted, present techniques do not necessarily yield a dry laid fibrous web that has all of these various properties. For example, the insertion of a scrim into a web does not necessarily improve the bulk or stretch characteristics of the web product, even though the web may be slightly stronger.
Similarly, the addition of an adhesive or cohesive bonding agent to the web product may enhance the strength of the web product, but bonding is difficult to perform effectively and does not necessarily increase the bulk of the web. For example, when the adhesive or cohesive bonding agent is added to the web, care must be taken to insure that the cellulosic web is not bonded to the forming wire and that the forming wire is not contaminated by the bonding agent.